This replaces the webassets build for the front-end JavaScript
and CSS with Gulp + Browserify. webassets continues to be used but
only to serve the assets, not to generate them or keep
track of dependencies.

 * Use CommonJS for all JS dependency imports rather than relying
   on Window globals. This makes dependencies more explicit
   and avoids the need to specify dependencies explicitly
   in the build tool, since they can be statically analyzed
   via the require graph.

 * Remove the webassets custom filters for Browserify and
   CleanCSS.

 * Put all generated JS/CSS/font/image assets in
   build/{images,fonts,styles,scripts}

 * Replace compass with node-sass + compass-mixins for building
   the SCSS files. We were not relying heavily on compass
   functions, many of them were used only for vendor prefixing
   which is now handled by autoprefixer, so we can remove the
   Ruby/compass dependency and substitute node-sass quite easily.

Add a first pass at a releaser script

Decouple transaction manager from database session

Fix annotation tag links

The ng-href directive does not treat its contents as
an Angular expression.

Fixes a regression introduced in e334fea0241282

Randomize websocket reconnects

Currently, if the websocket connection fails, then we will always
immediately attempt a reconnect. This can easily contribute to a
thundering herd problem if all WebSocket clients (or even a large
portion of them) are disconnected simultaneously.

This commit ensures that an aborted connection always results in at
least a 1s-2s (randomized) delay.

The client websocket code will automatically attempt to reconnect on
error or disconnection. This commit:

- Randomises the delay before reconnection
- Wait two seconds before attempting to reconnect (meaning the real
  delay will be between 2 and 4 seconds) -- this is an attempt to spread
  out reconnections over a longer period.
- Makes it stop retrying after 10 attempts (i.e. roughly 30 minutes)

Copy changes to Toggle or Resize Sidebar

Simplify routing

Fix styling of heading on 404, 5xx and Unsubscribe pages

This is a partial revert of 47bf5e8b5a123a9a5f1822e2bc84e5477aed6293

These pages use elements with both styled-text and page
classes applied and the result is currently source-order dependent.

Pending a refactoring of these styles, this reverts the @import
order change.

Annotation card & groups list style cleanup

Move /api/token endpoint into application

Using @extend with a class declared in a different source file
prevents local reasoning about the final set of rules
that will apply for a class because that depends on
what order the components are included.

See http://csswizardry.com/2014/11/when-to-use-extend-when-to-use-a-mixin/
for additional reasons to avoid @extend in most cases.

 * Make the .scss file names consistent with the names
   of their components for <annotation>, <thread>
   and <markdown>.

 * Sort component includes alphabetically and use relative
   paths. Although SASS technically doesn't care about
   relative paths, it makes the code style more consistent
   and also provides consistency with the JS code.

 * Move app-specific component style includes out of
   common.scss into app.scss

Rename style to signin-control-menu to match
the name of the associated component.

Move styles for the <group-list> and <signin-control>
components out of app.scss and into the appropriate
SCSS files.

Do not clear selection and reset search when creating a reply

Don't open "welcome page" when installed by admin policy

The purpose of clearing the selection was to ensure
that the new annotation was immediately visible.

Clearing the selection when creating a reply to
a selected annotation is not necessary because the reply
is part of an already-visible thread.

The logic for clearing the selection and search in the sidebar
when creating a new annotation was incorrectly being triggered:

 a) On the stream, where creating new annotations
    is not possible except for replies and
 b) For replies. The selection should only be cleared in the sidebar
    when creating a new annotation with a location on the page.

This commit addresses the first issue by moving the logic
for clearing the selection to the sidebar's controller.

Upgrade to Angular 1.5.0

Angular 1.5 introduces '<' as a way of specifying
that an isolate scope property is an input (one-way) binding.
Note that this is different from '::' (one-time) bindings from
ng 1.3.

See http://angularjs.blogspot.co.uk/2016/02/angular-150-ennoblement-facilitation.html
for details.

The principle benefit is making it obvious when looking
at the definition of a component whether a property is an input
or whether it is a binding that the component might write to.

The only change required was to fix an issue in <excerpt>
where the optional 'animate' and 'collapse' properties
were not correctly marked as optional, triggering
an internal error.

Annotation test cleanup

Scrollable groups list

This commit ensures that the groups list is scrollable when it is forced
to be smaller than the viewport due to the number of groups in it.

It's not an ideal solution, as in some contexts there isn't much of a
hint to the user that the widget is scrollable. It probably beats the
existing behaviour, though.

Fixes #2971.

I'm about to use this in a calculation elsewhere.

Angular's documentation for inject() involves a bunch of silly
boilerplate. This adds a utility function which wraps the inject()
function to provide a less verbose way of getting at ng modules
in tests.

Also make all of the fixtures pure functions and move
the logic for setting up the drafts fake into the
createDirective() function in the annotation tests.

Where a fake service/filter is not accessed directly
by any tests, make it local to beforeEach().

This reduces the surface area of globals exposed to all tests.

There were two describe('AnnotationController') blocks
containing very similar code.

Remove the tests from the second block which duplicated
those in the first and merge the others.

 * Also remove unused 'momentFilter' dep

Convert filters in the annotation directive to plain functions

The annotation directive used a set of filters for formatting
document domains, titles and usernames.

Converting these to plain functions eliminates a bunch of boilerplate
and as noted at https://www.binpress.com/tutorial/speeding-up-angular-js-with-simple-optimizations/135
is a small performance optimization.

Make annotation directive more consistent with other directives

 * Make it an element directive and use the existing utility
   functions for instantiating them in tests
 * Use '=' bindings for input properties and 'on<EventName>' names
   for events
 * Remove unused 'showReplyCount' input property and the
   shouldShowNumReplies() function which was only used
   as the argument to this property.